The present invention relates to a fuel injector for pressurizing fuel supplied to a nozzle by means of oil pressure.
FIG. 1 shows a fuel injector unit in the prior art. When a directional control solenoid valve 70 is at an off state, a pressure chamber 71 is connected via a check valve 72 with an accumulator 73 and a pump 74, and thereby fuel of a tank 75 is supplied to the pressure chamber 71. Also, an upper cylinder 76 is connected with the tank 75, and thereby fuel of the upper cylinder 76 is returned to the tank 75. After fuel has been supplied to the pressure chamber 71, the directional control solenoid valve is changed to an on state. With the on state of the directional control solenoid valve 70, the upper cylinder 76 is connected with the accumulator 73 and the pump 74, and thereby fuel is supplied through the directional control solenoid valve 70 to the upper cylinder 76. By this, a piston 77 and a plunger 78 are pushed down, and fuel of the pressure chamber 71 is pressurized and supplied to a nozzle 79. With a horizontal hole 80 of plunger 78 placed to oppose a groove 82 of a lower cylinder 81, fuel of the pressure chamber 71 is returned through a vertical hole 83, the horizontal hole 80 and the groove 82 to the tank 75, and thereby a fuel injection comes to an end.
According to the aforementioned injector unit, when the horizontal hole 80 of the plunger 78 opposes the groove 82 of the lower cylinder 81, pressure of the pressure chamber 71 drops suddenly. Because of this, the piston 77 and the plunger 78 drop at high speed until the piston stops by bumping against the bottom face of the upper cylinder 76 and the plunger 78 stops by bumping against the bottom face of the pressure chamber 71. As a result, considerable noise and vibration are generated.